You are correct that the only new idea here is the gravitational force being used in place of physical contact. Also, this method would only be practical for vary small asteroids with at least a few years notice. What has surprised me is the way it seems to have been seen as some kind of anti heavy lift pro JIMO manifesto. Actually I don’t even know what JIMO is but I assume it is some kind of NEP (Nuclear Electric Propulsion). Now the ONLY mention of NEP in the paper is this innocuous statement:
"The total impulse needed for rendezvous and deflection is too large for chemical rockets, but is achievable by 20 ton class nuclear-electric propelled spacecraft proposed by NASA. Regardless of the propulsion scheme, a docked asteroid tug needs an attachment mechanism since the surface gravity is too weak to hold it in place."
Notice that it says, "regardless of propulsion scheme". It is true that the popular press accounts of it prominently featured pictures of NEP spacecraft, but I would think by now that we would have all learned to check original source material before believing the press.

Just out of curiosity, what method do you propose for deflecting larger asteroids with less notice? The old Project Icarus atomic bomb method?

You are right about the mass. The corect value is 8.38E9 kg, not 6.38E9.

Nuke it from orbit - it's the only way to be sure Posted on: Tue Nov 15, 2005 7:54 pm

Sorry for not replying to this sooner. Project Icarus - for the biggest asteroids I don't see many other choices working (or at least not significantly less controversial ones). It's interesting to me that the actual amount of energy which is needed in principle to deflect these asteroids is very modest. The gravitational binding energy is small, approximately G*rho^2*16/15*pi^2*r^5 which often only amounts to a matter of few gigajoules for Apophis sized asteroids. Additionally the KE involved in a deflection is only tens of times bigger. This might suggest that the total amount of mechanical energy needed to part and deflect the pieces of a weak asteroid in a short time might not necessarily be overwhelming even for chemical/mechanical schemes. But a scheme that does this doesn't appear to be compatible with reasonable amounts of mass, particularly without dispersing part of the asteroid (which is the part you really want to avoid).

One other controversial method of deflection (for obvious reasons) is an Orion scheme which might be expected to work on a large monolithic asteroid. Straightforward variants of that are already rather disadvantaged in specific impulse however, and I'm still somewhat unconvinced that a pusher plate could survive very many cycles but I could be wrong.

Schemes with modest levels of dispersal generally spread material predominantly along the length of the pre-existing orbit and will probably not be at all effective for large asteroids in terms of reducing the negative consequences to Earth. As much as I like the idea of fierce meteor storms, even less drastic activities are likely to produce those.

Total vaporization is basically not a credible proposal unless you want to go to extreme overkill (in terms of heat input) on rather small asteroids. It would also have to function from well within the body of the asteroid to generate sufficient shock-heating which is a considerable problem with bodies possessing mechanical strength.

On one side we have publi.. and nihiladrem (84 posts, none of which have said what his qualifications are, but at least he has demonstrated some technical proficiency)

On the other side we have two men whom work for NASA, have flown in space, have a formal scientific education....

--And have never designed a spacecraft.

How about giving Stan Borowski a call at NASA Lewis, and asking him what he thinks of nuclear electric systems. I find him a bit more believable myself. The nuclear thermal advocates like Stan are being ignored and someone needs to stick up for them.

publi, he's got a point: you speak as if you are an established authority, yet you've never done a thing to establish that authority. At least I bug on out when I see that it's starting to go over my head...

Since nothing in the idea says we don't need heavy lift, and since you yourself said it would almost certainly require heavy lift to launch it, why are you so hostile to the whole idea? Don't like NEP? Make it SEP! Mass too small? Make it bigger and use a bigger heavy lift launcher.

My guess is that they have fallen for the old "We don't need HLLV" BS as touted by the EELV hacks and just want a weak 20 ton craft to slowly move out of Earth-Moon. It seems to me to be just another attempt to undermine Griffins heavy-lift mandate.

And even I can ride in a heavily automated Soyuz, same as ED LU. I am more interested in learning from Chief Designers, not astronauts who undermine their boss.

spacecowboy wrote:

publi, he's got a point: you speak as if you are an established authority, yet you've never done a thing to establish that authority. At least I bug on out when I see that it's starting to go over my head...

That doesn't mean you can't question things. What authority does an astonomer have with vehicle design?

None.

Same with being an astronaut.

MY point is that we should be asking what folks like Stan Borowski and others think about this approach. We're taxpayers, our money went to ED Lu's little trip, and that alone gives you, me and anyone else the right to question the methods he has proposed.

Last edited by publiusr on Wed Nov 16, 2005 4:44 pm, edited 1 time in total.

That doesn't mean you can't question things. What authority does an astonomer have with vehicle design?

None.

Same with being an astronaut.

I do question things, until the content of the discussion reaches an amount of technospeak at which point my questions are rather pointless, since I can't understand enough to formulate in my mind what it is that I can't understand.

And, to be honest, I'd think that the astronomer has a fair amount of authority over the vehicle design, since it's his payload that it's being built for (granted, he wouldn't know ISP from LH2, but he has to determine the payload capacity), and the astronaut has a lot of authority: he's the sucker that gets strapped on top of the thing. I agree with Kelly Johnson (who personally flew every single one of his creations, including the SR-71), if you don't get the hell scared out of you at least once per year, you're going to be worthless as an engineer.

Because I did my sums. The idea of using gravity as a tow line is valid and will work.

I think publiusr has doubts about the inherent reliablitiy of NEP (fairly complex with lots of possible points of failure and has to carry on working for a long time) rather than the gravity part of the tug. NTR would need to be heavier than NEP (though not for the 'special' case of Apophis). As Publi states, NTR has been practically demonstrated several times and is known to work.

If you had paid attention to my longer post, you will note that an NTR or large conventional stage could also serve as a gravity tractor

And if you had paid any attention to several of my posts you would know that I never dismissed the idea that an NTR or large conventional stage could also serve as a gravity tractor. In fact, just in case you still haven't got it, I do support that idea.

"The total impulse needed for rendezvous and deflection is too large for chemical rockets, but is achievable by 20 ton class nuclear-electric propelled spacecraft proposed by NASA."You are right about the mass. The corect value is 8.38E9 kg, not 6.38E9.

Anybody can make mistakes in math.

Lu and Durda seem to still be hinting at NEP, even though they said that any craft could be used. If you have kept up, you know that JIMO itself was getting to be quite large. My only point was that I thought NEP is a distraction. I would like to see my tax dollar used to build HLLV and launch a simple chemical tractor, as opposed to a Delta IV launched NEP that may not be buildable any time soon.